I'm not the only HN reader who claims to use a different email alias for each recipient, but mail user agents require me to remember to set the return address manually to the right alias on each outgoing message and risk leaking the wrong one if I forget. Some kind of email middleware that maintains a mapping from recipients to aliases and automatically slaps the right alias onto each outgoing message seems like it should be feasible for a single developer, but I can never find the motivation to do it myself. Apologies if I'm overlooking some well known application or service that already does.